Interpreting direction of motion from velocity-time graph | AP Calculus AB | Khan Academy

- [Instructor] An object
is moving along a line.

The following graph gives the
object's velocity over time.

For each point on the graph,

is the object moving forward,
backward, or neither?

So pause this video and see
if you can figure that out.

All right, now let's do this together.

And so we can see these different points

on this velocity-versus-time graph.

And the important thing to realize is

is if the velocity is
positive, we're moving forward.

If the velocity is negative,
we're moving backward.

And if the velocity is
zero, we're not moving

either forward nor backwards,

or neither forward nor backwards.

So right over here we see

that our velocity is positive.

It's a positive two meters per second.

So that means that we are moving forward.

Now, over here our velocity
is zero meters per second.

So this is neither.

Now, over here our velocity

is negative four meters per second.

So one way to think about it

is we're moving four
meters per second backward.

So I'll write backward.

Now, this is interesting, this last point.

'Cause you might be tempted to say

all right, I'm oscillating.

I'm going up.

Then I'm going down.

Then I'm going back up.

Maybe I'm moving forward here.

But remember, what we're
thinking about here,

this isn't position versus time.

This is velocity versus time.

So if our velocity is negative,
we're moving backwards.

And here our velocity is still negative.

It's becoming less negative,
but it's still negative.

So we are still moving,

we are still moving backward.

If we were at this point right
over here or at this point,

then we would be moving forward

if our velocity were positive.